Reverse angle thread system for containers

ABSTRACT

In a container for holding fluids having a neck portion through which the fluid is poured and a head portion, or cap which threadedly engages the neck portion, a thread system wherein the neck, or male threads are made of a relatively deformable plastic material, such male threads having a reverse downward angle and having parallel upper and lower edges, and the cap, or female member, being made of a harder less deformable material and having interengaging upward angled threads, the upward angle of the female member being greater than that of the male member such that upon threaded engagement the male threads hook within the female threads and are stressed into a strengthened engagement.

white States Patent [151 3,640,416 Temple Feb. 8, 1972 [54] REVERSEANGLE THREAD SYSTEM FOR CONTAINERS Primary Examiner-M. Henson Wood, .Ir.Assistant Examiner-Thomas C. Culp, Jr.

[72] Inventor: John J. Temple, 255 Kossuth Avenue, Mil- I l mont Park,Pa. 19033 A Paul [22] Filed: Oct. 16, 1970 [57] ABSTRACT [21 A N 81,279In a container for holding fluids having a neck portion through whichthe fluid is poured and a headportion, or cap which threadedly engagesthe neck portion, a thread system wherein ((zjll the neck or malethreads are made ofa relatively deformabie plastic material, Such malethreads having a reverse downward [58] Field at Search ..2l5/43, 220/39,15 l/2ll;ll,/22l2[l3 angle and having parallel upper and Iowa, edges,and the cap or female member, being made of a harder less defonnablematerial and having interengaging upward angled threads, the [56]References cued upward angle of the female member being greater thanthat of UNITED STATES PATENTS the male member such that upon threadedengagement the male threads hook within the female threads and arestressed 3,589,550 6/ i971 Rossmann ..220/39 R into a strengthenedengagement. 3,189,072 6/1965 Starr .220/39 R X 3,173,569 3/1965 Craig..220/39 R 7 Claims, 3 Drawing Figures \w F 25 I PMENIED rm 8m INVENTOR.

John J. TernpIe Wv-M A TORNFYQ REVERSE ANGLE THREAD SYSTEM FORCONTAINERS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an improvement in threaded closure systems forplastic containers utilized for high-strength applications and, moreparticularly, to an improved thread system which strengthens its lockingengagement as the components are threaded together.

2. Description of the Prior Art In many applications, plastic-typecontainers which are provided with threaded closure means, are utilizedfor containing liquids which give rise to considerable pressures withinthe vessel. In other applications, the deformable nature of the plasticcontainer is such that, under the stresses of handling, loading, andtransporting considerable pressures are generated within the vessel.Such pressures exert force on the threaded closure means, whichgenerally consist of a threaded neck, or nozzle, and a threaded capwhich interfits with such neck. It is necessary that the thread system,or assembly, be able to accommodate such internal pressures. The generalsource of failure in thread systems such as utilized for the aboveapplications is that of nonuniform stress applied to the female member,or cap. In the standard 60 thread system, maximum stress is transmittedradially through the apex of each thread, causing localized strain atthe apex of the receiving groove. Further, when internal pressure tendsto force the cap off the container, the 60 thread of the neck provides arestraining force on the cap which has a radially outwardly directedcomponent, which is the reverse of what is desired. Accordingly, threadconstructions in containers designed to retain high pressures havegenerally had either overdesigned cross sections, or varioussupplemental mechanisms to strengthen the thread system.

An improvement over the standard screw design is that of thebuttress-type thread, which provides a flat engaging surface normal tothe axis of the container. In this thread system, the restraining forcehas no outward component, and in this regard represents an improvement.Buttress threads, and adaptations thereof, have been widely used in theart. See, for example, US. Pat. No. 3,487,442, illustrating animprovement to a buttress thread system. The buttress thread provides animprovement against shear due to axial stress, but does not improve overthe standard design in providing against radial stress.

Another technique used in the art is to construct one of the closureelements of a relatively soft or deformable material, and the other of aharder material, so as to provide interengaging compression forces tostrengthen the engagement of the two elements. See, for example, US.Pat. Nos. 2,950,033 and 2,962,185. However, in these and other threadsystems, there is no means within the thread structures themselves toprovide locking forces holding the male and female members togetherunder the force of pressure from within the container. Thus, while thethread systems are tightly engaged and not easily unscrewed, there is nogripping or locking action in such structures to prevent fracture due tointeraction forces between adjacent thread surfaces.

SUMMARY OF THE INVENTION It is an object of this invention to provide athread system for containers wherein the threads interengage in a mannersuch as to restrain both radial and axial forces.

It is a further object of this invention to provide a thread system forcontainers, which thread system is able to withstand internal containerpressures of great magnitude.

It is a further object of this invention to provide a thread system forcontainers wherein the male and female members interlock in a mannersuch that thread stress is distributed evenly between such members.

Accordingly, this invention provides an improved thread system for acontainer having a neck member with an opening therethrough, and a capwhich is screwed into a complementary threaded engagement with the neck,wherein the neck is made of a relatively deformable soft plasticmaterial and has threads extending radially outward on the outer surfacethereof, each thread being inclined at a downward angle from a planenormal to the axis of the neck, and the cap, made of a harder plasticmaterial, has receiving threads adapted for interengagement with theneck threads, the cap threads being inclined upward from the planenormal to the axis at an angle reverse to that of the neck threads, suchthat upon threaded engagement the relatively deformable neck threads arepushed into locking engagement with the cap threads. The reverse angledthreads permit a locking engagement of the male and female closuremembers which strengthens the closure against internally generatedpressures. By making the angle of the neck threads less than that of thecap threads, the neck is stressed into a tight engagement with the cap.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of thethread system of this invention, showing the container neck and cap inthreaded engagement.

FIG. 2a is an enlarged cross section of the cap threads of thisinvention.

FIG. 2b is an enlarged cross section of the neck threads of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. I, thethread system of this invention is shown, having the container neck andcap in threaded engagement. Container 20 has an opening 25 through anupper neck portion which has downward angled threads 21, as also shownin FIG. 2b. The threads have parallel upper and lower surfaces, thesurfaces being at an angle of 29 with respect to a plane nonnal to theaxis of the neck, in the preferred embodiment. The cap 23 has threadswith parallel upper and lower surfaces, the surfaces being inclinedupward with respect to a plane normal to the axis of the cap, the angleof inclination being 30 in the preferred embodiment.

The cap is made of a relatively hard nondeformable plastic substance,such as polystyrene, while the container neck, or male member, is madeof a softer, more deformable material, such as polyethylene. Theseexamples of relatively hard and soft plastic materials are given forillustrative purposes only, it being understood that the invention maybe practiced with any two plastic materials having relatively soft andhard properties with respect to each other.

When threaded together, as shown in FIG. 1, the threads of the twoelements hook within each other, being of reverse angles with respect tothe plane normal to the axis of the container and cap. Due to thereverse angle geometry, as contrasted to the standard 60 and buttressthread geometries, adjacent threads dont merely engage, but actuallyhook each other in a locking and mutually supporting configuration.Also, due to the lesser angle of the relatively soft plastic neckthreads being forced into the greater angled receiving threads of theharder plastic cap, there is a further tightening and strengthening ofthe thread system.

When thus threaded together, the two elements provide a greater strengththan prior art thread systems, because of the nature of the interlockingof the threads. When the pressure F within neck 25 tends to push cap 23off container 20, the con tainer threads 21 provide a reaction forceagainst cap threads 24, which reaction force has a radially inwardcomponent as well as an opposing axial component, as indicated by thereaction force vector F,. It is thus seen that the reverse angle threadacts to clamp the cap inwardly in response to axial pressure, whichaction provides a great advantage over prior art thread systems. It isto be emphasized that the invention provides greater strength in thethread system itself. Sealing of the cap to the container neck is ofsecondary importance, as the top opening of the container is usuallysealed by a gasket 26 located in the bottom of the cap.

It is to be understood that the reverse arrangement of threads is thefeature that causes the hooking interengagement of cap and neck, andthat the threads may be angled upward instead of downward, or themale-female roles of the container neck and cap may be reversed, withinthe spirit and scope of this invention. Further, while the thread anglesof 29 for the neck and 30 for the cap are preferred angles, and angulardifference in the range of 1 to 5 may be utilized in the practice ofthis invention. Further, any reverse angle in the range of 25 to 45 forthe cap and neck threads, provides the strength and locking features ofthis invention.

Due to the nature of the threads as described, it is understood thatthis invention is not applicable to metal containers, but that thethreads must be molded of plastic. However, the container neck and capmay be made of any suitably deformable and moldable material. Theimproved thread assembly, as described above, is extremely useful incontainers for acids, toxic fluids, beverage containers, andparticularly any substance where internal container pressures may begenerated, and safety is an important factor.

I claim:

1. A container assembly comprising:

a. a cylindrical neck member having an opening therethrough and threadsaround the outer surface thereof, the threads having parallel upper andlower surfaces inclined downward at a first angle from the plane normalto the axis of said neck member;

a closure cap member in complementary threaded engagement with said neckmember, having threads around the inner surface thereof, such threadshaving parallel upper and lower surfaces inclined upward at a secondangle greater than said first angle; and

c. said two elements when threadedly interengaged hooking each othersuch that when pressure within said container assembly is exertedagainst said cap member, said neck threads transmit a reaction forceagainst said cap threads having axial and radially inward components.

2. The container assembly as described in claim 1 wherein said neckmember is comprised of a relatively soft plastic material, and saidclosure member is comprised of a relatively hard plastic material.

3. The assembly as described in claim 2 wherein the angular difierencebetween said first and second angles is in the range of 1 to 5 4. Theassembly as described in claim 3 wherein said second angle is 30 andsaid first angle is 29 5. The assembly is described in claim 3 whereinsaid second angle is in the range of 25 to 45.

6. A container assembly comprising:

a. a first cylindrical member having male threads;

b. a second cylindrical member having female threads;

0. said members being in complementary threaded engagement and having acommon axis, and said threads being at reverse angles from the planenonnal to said axis such that an axial force exerted upon one of saidmembers is opposed by a reaction force transmitted through the threadsof the other, said reaction force having an opposing axial component anda radially inward component.

7. The assembly as described in claim 6 wherein said male threads areinclined at a first angle from said plane, and said female threads areinclined at a second angle from said plane.

1. A container assembly comprising: a. a cylindrical neck member havingan opening therethrough and threads around the outer surface thereof,the threads having parallel upper and lower surfaces inclined downwardat a first angle from the plane normal to the axis of said neck member;a closure cap member in complementary threaded engagement with said neckmember, having threads around the inner surface thereof, such threadshaving parallel upper and lower surfaces inclined upward at a secondangle greater than said first angle; and c. said two elements whenthreadedly interengaged hooking each other such that when pressurewithin said container assembly is exerted against said cap member, saidneck threads transmit a reaction force against said cap threads havingaxial and radially inward components.
 2. The container assembly asdescribed in claim 1 wherein said neck member is comprised of arelatively soft plastic material, and said closure member is comprisedof a relatively hard plastic material.
 3. The assembly as described inclaim 2 wherein the angular difference between said first and secondangles is in the range of 1* to 5* .
 4. The assembly as described inclaim 3 wherein said second angle is 30* and said first angle is 29* .5. The assembly is described in claim 3 wherein said second angle is inthe range of 25* to 45* .
 6. A container assembly comprising: a. a firstcylindrical member having Male threads; b. a second cylindrical memberhaving female threads; c. said members being in complementary threadedengagement and having a common axis, and said threads being at reverseangles from the plane normal to said axis such that an axial forceexerted upon one of said members is opposed by a reaction forcetransmitted through the threads of the other, said reaction force havingan opposing axial component and a radially inward component.
 7. Theassembly as described in claim 6 wherein said male threads are inclinedat a first angle from said plane, and said female threads are inclinedat a second angle from said plane.